countryCode method
Returns Play billing country code based on ISO-3166-1 alpha2 format.
See: https://developer.android.com/reference/com/android/billingclient/api/BillingConfig See: https://unicode.org/cldr/charts/latest/supplemental/territory_containment_un_m_49.html
Implementation
@override
Future<String> countryCode() async {
final BillingConfigWrapper billingConfig = await billingClientManager
.runWithClient((BillingClient client) => client.getBillingConfig());
return billingConfig.countryCode;
}